1. Field of the Invention
The present invention relates to various automotive piping, especially a highly heat-resistant resin tube suitable for fuel system piping for an automotive engine, and to a method of fabricating the resin tube.
2. Description of the Related Art
Various piping arrangements are provided on an automobile. Among these, some are constituted by resin tubes. Resin tubes are lightweight and easy for handling as compared to metallic tubes and rubber tubes. Further, the resin tubes also have an advantage of simple processes for connection by use of resin connectors or the like. Moreover, resin tubes tend to be low in terms of manufacturing costs as compared to metallic tubes and rubber tubes.
Nylon 11, Nylon 12 and the like are used for the resin tubes of automotive piping. These materials have an advantage of high flexibility, whereby freedom of piping shapes is brought about.
The automotive piping to be provided particularly inside an engine room is frequently exposed to high temperature. Accordingly, such piping is required to possess sufficient heat resistance and strength. In addition to heat resistance and strength, the automotive piping is required to possess oil resistance for application to oil system piping, and fuel resistance for application to fuel system piping.
For example, regarding vapor fuel piping installed inside a fuel tank, the piping after installation in the tank is exposed to a high-temperature atmosphere of about 180xc2x0 C. during the painting and drying processes of the tank. Therefore, there is a problem in that the vapor fuel system piping tends to be deformed by heat.
The above-mentioned Nylon 11 and Nylon 12 do not possess adequate heat resistance or airtightness for application to fuel system piping for an automotive engine.
Meanwhile, Nylon 66 is known to be a heat-resistant material. However, since the Nylon 66 has poor moldability, it is difficult to process the Nylon 66 by means of extrusion molding and the like. Moreover, since the Nylon 66 has poor flexibility, the Nylon 66 cannot provide freedom of piping in an automobile.
The present invention has been accomplished to solve the above problem, and it is an object of the present invention to provide a highly moldable and highly heat-resistant resin tube for automotive piping and to provide a fabricating method of the resin tube.
The first aspect of the present invention provides a resin tube for automotive piping comprising: Nylon 66 having a viscosity number within a range of 240-370 in a measurement of a 98% concentrated sulfuric acid solution at 25xc2x0 C.; Nylon 6 having a viscosity number within a range of 170-340 in the measurement; and a plasticizer, wherein the resin tube is made of a composite as a mixture thereof prepared with a proportion in a mass ratio of the Nylon 66:the Nylon 6:the plasticizer to be within a range of 100:5-50:3-20.
According to the first aspect of the present invention, the Nylon 66 is used as a base material, the resin tube has excellent heat resistance, fuel resistance and oil resistance. Accordingly, the resin tube is also applicable to fuel system piping for an automotive engine, for example. Addition of the Nylon 6 and the plasticizer to the Nylon 66 achieves higher flexibility in comparison with the single Nylon 66. Therefore, the addition enables use of the resin tube in piping in a small space or in piping with complicates shapes. Although it was difficult to carry out extrusion molding with the single Nylon 66, addition of the Nylon 6 and the plasticizer to the Nylon 66 makes it possible to have formation such as extrusion molding by use of a normal extruder machine. Since it is unnecessary to use special engineering plastics such as Nylon 46 or polyphenylene sulfide (PPS), material costs can be reduced as well.
The second aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, wherein the resin tube is made of a composite as a mixture thereof prepared with a proportion in a mass ratio of the Nylon 66:the Nylon 6:the plasticizer to be within a range of 100:10-40:5-10.
According to the second aspect of the present invention, it is possible to impart flexibility, moldability and the like additionally to the resin tube without affecting performances thereof such as heat resistance, fuel resistance and oil resistance.
The third aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, wherein the viscosity number of the Nylon 66 is within a range of 270-340.
According to the third aspect of the present invention, it is possible to impart flexibility, moldability and the like additionally to the resin tube without affecting performances thereof such as heat resistance, fuel resistance and oil resistance.
The fourth aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, wherein the resin tube is formed into a straight tube.
The fifth aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, wherein the resin tube is formed into a bellows.
The sixth aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, wherein the resin tube is formed into a multilayer tube in combination with other resin.
The seventh aspect of the present invention provides the resin tube for automotive piping according to the first aspect of the present invention, further comprising: an additive for use in resin materials.
The eighth aspect of the present invention provides a method of fabricating a resin tube for automotive piping comprising the steps of: mixing Nylon 6 having viscosity number within a range of 170-340 in a measurement of a 98% concentrated sulfuric acid solution at 25xc2x0 C., and a plasticizer; preparing a resin composite by mixing the mixture of the Nylon 6 and the plasticizer with Nylon 66 having viscosity number within a range of 240-370 in the measurement; and forming the resin composite into a tube by extrusion molding.
According to the eighth aspect of the present invention, the Nylon 6 and the plasticizer are mixed in advance and the mixture is added to the Nylon 66. Therefore, it is possible to mix the Nylon 6 and the plasticizer uniformly and easily with the Nylon 66.
Addition of the Nylon 6 and the plasticizer to the Nylon 66 effectuates easy and efficient molding of the resin tube by normal extrusion molding.